Process for dewaxing oil



Oct. 22, 1940. u. B. BRAY PROCESS FOR DEWAXING OllL Filed Now/.'27, 1931 2 sheets-sheet '1 Oct. 22, 1940. u. B. BRAY PROCESS FOR DEWAXING OIL 2 Sheets-Sheet 2 Filed Nov. 27, 1931 U/rzc qly BY M6 ATTORNEY.

INVENTOR. B Br' n QQN N .www

Patented Oct. 1940 UNITED STATES PATENT OFFICE PROCESS FOR DEWAXING OIL Ulric B. Bray, Palos Verdes Estates, Calif., asi* signor to Union i! Company 4of California, Los Angeles, Calif., a corporation of California Application November 27, 1931, Serial No. 577,593

8 Claims.

This invention relates to a process for the separation from petroleum of those hydrocarbons which are normally solid at ordinary tempera` l0 amorphous or crystalline wax, or other gummy substances from lubricating oil, it may be utilized in the treatment of any other petroleum fraction Where it is desirable to separate the oil-from the foregoing substances. Subject matter disclosed herein but not claimed is` claimed in the following, copencling application `and patents:

` Serial 190.466,189, claiming dewaxing with a i liqueed normally gaseous hydrocarbon; Serial No. `597,419, tiled` March 7, 1932, `claiming deg, asphalting with distillation; Serial No. 705,910, filed January 9, 1934, a division `of Serial No. 466,189, claiming wax separation 'under controlled pressures, centrifuging, alternate chilling and special features of construction; Serial No.

25 707,641,- filed January 22, 1934, claiming sepa- `,ration of asphalt or kindred material in conjunction with heating; Serial Nos. 721,602, led April 20, 1934, and 749,649, filed October 23, 1934, both divisions of Serial No; 466,189 and i 30 claiming treatment with butane; Patent No.

1,944,491 claiming separation of asphalt and Wax; Patent No. 1,949,989, claiming asphalt separation; Patent No. 2,006,098, claiming chemical treatment in conjunction withpropane `treat- `35I ment; and Patent No. 2,031,204, claiming propane treatment in conjunction with the use of heavier solvent materials. y

Many crude oils from` which lubricating oil is produced contain paraflin or wax. It is found 40 associated with the lubricating oil fractions of paraiiin base crude oil andwith the lubricating oil fractions produced from many of the mixed base and asphalt base crude oils. `It is not only of doubtful lubricating value but limits the tem- 45 perature at which lubricants containing it may be used by congealing at the lower temperatures. Therefore, in `the productiony of lubricating oil from petroleum fractions" containing wax or parailin, it is customary,`at the present time, to remove asub-stantial portionoi the wax or paraiiin present in the oil in order to lower the temperature at which theiinal product congeal-s. The temperature at which an oil congeals is commonly `55 referred to as its pourpoint and this value is `cold settling process.

usuallyobtained` according to method 1397-30 of the American Society of VTesting Materials.

' Several methods well known inA the art are employed at present for the production of low pour point lubricating oil stock from petroleum `fractions which contain substances conges-ling at ,by the aid of brine circulated in coils located within the tank. The chilling process is carried out for a period of from to 50 hours until a temperature is reached at which there exists a substantial separation of the wax in the form of a slime or gel from the solution of oil. By al4 20 lowing the cold solution of oil containing precipitated wax to stand for a period of several Weeks` the precipitated waxA settles to the bottom of the i chilling tank. `Whilethis methodhas been used extensively for the separation of Wax from lu-` bricating oil it is objectionable `because of the cost of refrigerating the diluted oil over so long a period, furthermore because of the large tanlrl and refrigeration capacity required for the treatment of the oil and lastly onaccount of the usual poor separation obtained between the wax and the oil. y u vI Another method for deWaXing petroleum which hasbeen used to a large extent is known as the cold pressing process. Wax distillateproduced' 35 from those `fractions of petroleum distilling'` over between the approximate temperature limits of 450 `F. Zand 675 F. is chilled slowly to a temperature of about 15 to 30 F. whereupon the Wax present in the` oil `precipitates to form a product having a mushy consistency. The cold mushy mass is then pumped through a lilterl press under a pressure of 30D-350 pounds per square inch. The WaX present is collected upon the filtery and the oiliis recovered as apressed distillate relatively free from Wax. `When the oil under treatment contains a relatively large quantity of wax'it is sometimesnecessary to rechill and re-lter it in order to obtainan oil havingthe desired pour point. i The length of time 50 required to filter the chilled oil depends upon the crystalline structure of the Wax; A distillate which is poorly crystallized, i, e., with crystals -in the form` ofplates, or in which the Wax crystals are small requires a much longer' period of l- 55 tration than does a distillate in which the wax crystals are large and of needle structure. This process has found commercial application only in conjunction with oils having the wax present in a crystalline form, as so-called amorphous wax or micro-crystalline wax is extremely diicult to separate by iiltration from oil. Consequently oils containing amorphous wax cannot be treated on a commercial scale by this process. In Ythe production of the wax distillate the distillation step is usually sufficient to convert the wax from an amorphous to a crystalline state or more probably to destroy crystallization inhibitors, which changes afford quick separation of the wax from the chilled oil in the filter presses. However, in some cases, distillation of the wax is insuiicient to produce the proper crystalline structure required for practical iitration, in which case it becomes necessary to expose the wax distillate to a cracking operation.

Y Another process has been suggested which consists in diluting the oil containing` wax with such light petroleum hydrocarbons as gasoline, naphtha or kerosene, adding to the diluted oil a waxadherent material, chilling the mixture of oil and wax-adherent material with constant agitation until a temperature is reached which is suinciently low to cause the wax present in the oil to precipitate and collect upon the wax-adherent material and nally separating the substantially wax-freeoil by iiitration from the wax-adherent material and wax. Again this process is objectionable because of the long period of time required to obtain suitable wax separation from the diluted oil and also because of the large chilling and ltering capacity required to make the process commercially possible.

I have discovered that many of the disadvantages present in the foregoing processes which I have described may be overcome by removing the waxy constituents of petroleum according to the process which I am about to describe.

Paraln and wax are more soluble at low temperature in the heavy hydrocarbons, i. e., hydrocarbons of high molecular weight, than in the light hydrocarbons, i. e., hydrocarbons of low molecular weight. Thus the solubilities of these materials at low temperatures are greater in kerosene than in gasoline and appreciably greater in gasoline than in a light hydrocarbon such as liquid propane. When oils containing wax are dissolved in such solvents as kerosene or gasoline and chilled to a temperature of F. or lower, the wax present slowly precipitates out of solution. Consequently a long period is usually required to obtain substantial precipitation oi the Wax from solution.l Where lighter solvents are employed as diluents for the waxy oil, the period of refrigeration is materially lessened and the precipitation of the wax from solution is more complete. I have discovered that liquid propane is an ideal diluent for the precipitation of wax from wax bearing oil at low temperatures. Owing to its poor solvent power for wax at low temperatures, it is very desirable as a diluent in the precipitation of wax from waxy oils at low temperatures. It is especially desirable for this purpose because once the propane solution of waxy oil has reached the desired dewaxng temperature the wax present in the solution immediately precipitates out. Long periods of refrigeration which add greatly to the cost of dewaxing the oil are thus avoided.

I have discovered that wax which has been precipitated fromV a propane solution of waxy oil differs in physical structure from wax which has been precipitated from waxy oil dissolved in heavier solvents such as gasoline or naphtha.

Waxes which have been precipitated from gaso line or naphtha by chilling a residual waxy oil dissolved in these solvents are usually highly amorphous in structure. They are in the nature of gels or slimes and as such oier many dini-- culties in their removal from the chilled solution of oil and solvent. As has already been pointed out they are unusually hard to separate by ordinary ltration methods as the slimy wax forms an impervious layer upon the lter plate of the lter press which obstructs free movement of the dewaxed oil through the lter plate, and ltration is usually possible only if excessive amounts of lter aid are employed. Furthermore, the wax flocks or aggregations which are formed during the chilling operation will not settle out by cold settling methods sumciently to produce a nished oil of the desired pour point because of the slight diierence in the specic gravity between the solution of oil in the solvent and the wax. However, when the wax is precipitated by chilling waxy oil dissolved in propane it possesses a highly granular structure. While it may not be macrocrystalline in character yet it is unlike the Wax produced by chilling a waxy oil dissolved in naphtha or gasoline in that it appears to be composed of discrete particles.

Due to the granular structure which the wax possesses when precipitated from a chilled propane solution oi waxy oil it may be separated commercially from the propane solution of oil by ltration with none of the attending diiculties present when ltering waxy slimes from chilled gasoline, naphtha, or relatively heavy hydrocarbon solutions of oil. The granular structure of the wax precipitated from the chilled propane solution of waxy oil does not form the impervious film over the lter plate which is characteristic of waxy slimes or gels precipitated from chilled solutions of waxy oil dissolved in such solvents as gasoline or naphtha. Instead such granular waxes form a porous layer upon the filter plate through which the wax-free oil dissolved in sol-V vent may freely ow.

In some instances I find it advantageous to precoat the plates or the lter with such lter aids as diatornaceous earth, fullers earth, clay, wood ilour or sawdust prior to filtration. By depositing a thin layer of any of the foregoing materials upon the lter plate prior to passing the chilled mixture of propane and oil containing precipitated wax through the iilter I am able to obtain a more thorough separation of the granular wax from the oil dissolved in propane. In carrying out this type of operation I iirst mix a small quantity of the precoating materials such as diatornaceous earth, fullers earth, clay, woodilour or sawdust with liquid propane and pass this mixture through the filter. The precoating substance suspended in the liquid propane deposits itself in a thin layer over the lter plate and the propane is withdrawn from the lter press as a clear filtrate. The chilled oil dissolved in liquid propane carrying precipitated wax in suspension is now forced through the lter press and the precoating materials present on the lter plates aid in separating the wax from the propane solution of oil. While I may employ any of the foregoing materials as precoating substances for the lter press, I have found wood our to be especially well adapted for this purpose.

Furthermore, due to the difference in speciiic gravity between the precipitated granular wax and the propane solution of oil, I am able toobtain satisfactory separation of the precipitated wax and thesolvent solution of oil by` ordinary settling methods as contrasted with relatively unsatisfactory results incase heavier solvents, 4such as `naphtha orgasoline, are employed as diluents for the waxy oil. The long settling period necessary to obtain separation o-f the pre- I cipitated wax from the gasoline ornaphtha solution of oil is obviated by the substitution of liquid propane for the gasoline or naphtha as diluent. .Due ito the granular form in which the wax precipitates from `the chilled` propane solution of waxy oil and furthermore due to the difference in specific gravity between vthe precipitated Wax and the propane solution of oil, rapid separation by gravity may be obtained of the precipitated wax from the propane solution of oil. This makes possible the elimination of the large settling capacity which is necessary in the cold settling process for the separation of` wax from oil, The cold settling process is essentially a batch process; that is to say large volumes of waxy oil dissolved in such solvents as gasoline or naphtha are chilled to a temperature sufliciently low to precipitate Ia portion of the wax present, after which the mass is allowed lto remain in a quiescent state for several Weeks in orderto allow the wax to settle out. Owing tothe rapid rate at which the precipitated granular wax separates out of the cliilledoil dissolved in liquid propane, I am able to operate my l dewaxing process continuously. 'By continuously feeding a chilled mixture of wax and oil dissolved in liquidlpropane to an ordinary vapor tight settling chamber it is possible to separate the precipitated wax from the propane solution of oil. l i

Another advantage of using a liquid hydrocarbon as a diluent for the wax containing oil is that by allowing a portion of the solvent to vaporize under reduced pressureall the necessary refrigeration is obtained to chill the oil to the desired dewaxing temperature. rst dissolved under pressure in a light liquid e hydrocarbon. `A -portion of the light liquid hydroincludepropane, isobutane, butane, ethane, methane and mixtures thereof. These may be obtained by the rectification of casinghead gasoline bythe so` called stabilizing methode. They are i the overhead thus obtained. They are liquefied by compression and cooling in the conventional manner and drawnoff into pressure chambers where they are maintained in a liquid state until they `are used. A .typical analysis of such a solvent is 6.72% ethane,72.20% propane, 19.91% isobutane and 1.17% normal butano. I-Iereafter for convenience such a fraction will be referred to as propane However, it is to; beunderstood that I do not propose to limit myself to a solvent having `the foregoing composition as the percentage of the individual hydrocarbon members '151 of the solvent may vary more or less.

The waxy oil is l Itis therefore an object of my invention to precipitate granular wax from wax-bearing oil and separate said Wax fro-m said oil.

It is another object of my invention to precipitate granular Wax from wax-containing oil by the use ofa solvent and to separate Vsaid wax from theoil and solvent. l

It isanother object oi my invention to precipitate wax in a nely granulated form from wax-bearing oil by the use of liquid propane and subsequently to separte the wax, oil and propane from each other.

It is another object of my invention to precipitate wax from oil containing wax by the use `of liquid propane, separate said wax from said oil and propane -by the aid of a filter plate precoated with a filter aid and subsequently separate the substantially wax-free oil from the propane.

It is still another object of my invention to dissolve waxy oil in liquid propane under pressure, cool the waxy .oil dissolved in liquid propane to a temperature sufliciently low to precipitate granular wax by allowing a portion of the propane to vaporize under reduced pressure, separate the `wax from the oil dissolved in liquid propane and subsequently separate the propane from the substantially wax-free oil.

. It is still another Object of my invention to dissolve oil containing wax under pressure in liquid propane, and chill the propane solution of oil to a temperature sufficiently low to precipitate wax by vaporizing a portion of the propane under reduced pressure, impose sufcient pressure upon the cooled solution of oil and precipitated wax to prevent further vaporization of propane, separate the wax from the oil dissolved in liquid propane and subsequently separate the propane from the substantially wax-free oil.

Fig. 1 is a schematic arrangement of one form of apparatus for carrying out my invention.

Fig. 2 is a schematic arrangement of another form of the apparatus in which my process may be carried out.

Referring more .particularly to` Fig. 1, waxy oil above its congealing point in tank I is withdrawn through line 2, valve 3, line 4 and sent by means of pump 5 through line 6 into agitator 'I Where the waxy oil is dissolved in liquid propane coming from tank IIJ by means of line II, pump I2, line I3, valve I4 and line I5. The waxy oil clissolved in liquid propane passes from agitator 1 into separator 55 where any undissolved asphalt present in the oil is permitted to settle out and is withdrawn through valve 56 and line 5l. The waxy oil dissolved in liquid propane passes from separator 55 through line 8 into chiller 9. The waxy oil dissolved in liquid propane is cooled to a temperature suificiently low to precipitate a substantial portion of the wax present by allowing a portion of the liquid propane present to vaporize under reduced pressure through line I6 and valve I'I, from whence it passes to compressor I8, which forces it through line I9 to condenser 20 where it is liqueed and passes by means of line2I to propane storage tank I0. During the chilling operation in chiller 9, sufficient propane is vaporized to reduce the pressure within the Chiller to approximately atmospheric pressure.

The chilled solution of oil dissolved in liquid` Wood flour introduced through line 26|.

chamber 30 isincreased to a point suihciently high to cause all boiling or ebullition within this chamber to cease by maintaining suilicient pressure within chamber 30 by operation of pump 40. After the chilled oil in iiltering chamber 30 has remained in a quiescent state for a short period under sulcient pressure to inhibit boiling or ebullition, valve 3| is opened and the wax-free oil passes through filter plate 49 into line 32 from whence it passes to pump 33 which forces it through valve 53 and line 41 into heater 34, vaporizes all of the propane present by means of steam which is introduced through closed steam coil 43. The vaporized propane passes from heater 34 through line 35 to compressor 30 which forces it through line 31, valve 38, line 9 to condenser 23 where it is condensed and passes through line 2| to propane storage tank I9.

The dewaxed and propane-free oil in heater 33 is removed through valve 54 and sent by line to tank 46.

The Wax cake in iiltering chamber 39 is removed, after which another charge of chilled oil, containing precipitated wax from chiller 9, is introduced and the dewaxing operation is repeated.

As a modication of the foregoing process I sometimes iind it desirable to pr-ecoat filter plate 490i iiltering chamber 30 prior to introducing the chilled propane solution of oil and precipitated wax. Liquid propane from tank i9 passes by means of line to pump l2 which forces it through valve 22, line 23, to agitator 25 where it is mixed with such precoating materials as kieselguhr, diatomaceous earth, ullers earth, clay or The precoating material suspended in liquid propane passes through line 2S, valve 21, line 20 and line 29 into ltering chamber 30 where the precoating material is deposited in a layer upon plate 49. The propane is withdrawn through valve 3| and line `32 to pump 33 which forces it through line 50, valve 5| and line 52 to propane storage tank I0.

After the filter plate in filtering chamber 30 has been covered with a layer of precoating material, the chilled oil dissolved in propane carrying precipitated wax is withdrawn from chiller 9 through valve 39 and line 48 into pump 40, which forces it through line 4| valve 42 and line 29 into chamber 30 from whence it is forced through the precoated filter plate 49 which retains the pre cipitated wax and allows the propane solution of oil to pass freely through valve 3| and line 32 to pump 33 which forces it through valve 53 and line 41 to heater 34 where the propane is separated from the dewaxed oil.

Referring more particularly to Fig. 2, waxy oil from tank |00 at a temperature above its congealing point passes by means of line |02, valve |03 and line |04 to pump |05, which forces it through line |06 into agitator |01 where it is dissolved in liquid propane coming from tank H9 through valve line H2, pump H3, line ||4, valve |49 and line |96. The waxy oildissolved in liquid propane passes from agitator |01 into separator |59 where any undissolved asphalt present in the oil is permitted to settle out and is removed through valve |99 and line |6I.

The propane solution of waxy oil passes from separator |59 into line |98 from whence it passes into chilling tank |09. By opening valve l i5 and allowing a portion of the propane present in chilling tank |09 to vaporize, the temperature of the waxy oil dissolved in the liquid propane is lowered sufficiently to cause precipitation of theamarsi? wax. The vaporized propane is removable through line ||1 to compressor ||8 which forces it through line ||9 to condenser |20 where it is liquefied and passes by means of line |2| to propane storage tank l l0.

The chilled oil dissolved in propane carrying the precipitated wax is removed from chiller |09 through line |22, valve |23 and line |24 to pump` |25, which forces it through line |20 into the vapor tight wax separator |21. In order to prevent boiling or ebullition in the Wax separator during the wax settling operation, pressure is imposed upon the solution of oil. This is accom-A plished by maintaining pressure within the separator by pump |25. As the chilled mass in the wax separator remains in a non-ebullient state the wax settles out and is collected by vanes |30 which remove it through valve |32 and line |33. rIhe wax-free oil dissolved in propane is withdrawn from the separator |21 into line |35, valve |35, line |58 to pump |31 which forces it through line |39 into heater |39 where the propane present is vaporized by aid of steam introduced through closed steam coil |40. The vaporized propane passes out of the heater through line |4| to compressor |42 which forces it through line |93, valve |44, and line ||9 to condenser |20 where it is liquefied and passes by means of line |2| to propane storage tank l0. 'Ihe dewaxed propane-free oil passes from heater |39 by means of line |45, valve |45 and line |41 into tank |43.

As an example of the preferred method of carrying out my process Santa Fe Springs crude oil topped to a viscosity of 10|) seconds, (Saybolt Universal at 190 F., on stream) is withdrawn from tank |33 and mixed in agitator |01 with liquid propane Withdrawn from tank ||0 in the roportion of one volume of the topped crude oil to six volumes of liquid propane. The agitated mass is passed into settling chamber |59 where the asphalt precipitates out and is withdrawn through valve |99 and line IGI. The propane solution of waxy oil passes from the settling chamber |59 into chilling tank |09. Valve H6 is opened and propane is vapo-rized until the proportion of propane to oil is about four to one. By this time the temperature of the chilling tank will have fallen to about 35 F. if a reasonably pure liquid propane has been used. The vaporized propane in line ill is forced by compressor H3 through line H9 into condenser |20 where it is liquefied and'A passes into propane storage l lf3. The chilled propane solution of oil and precipitated wax is withdrawn from chilling tank |39 through line |22 and forced by pump |25 into the wax lseparator |21. By maintaining suiicient pressure upon the liquid in separator |21 all ebullition ceases, the wax present settles out and is removed by vanes |39 into line |33. The oil and solvent pass out of the wax separator through line |35 and are forced by means of pump |31 into heater |39 where the propane is separated from the oil with the aid of steam introduced through closed coil |49. The asphalt and waxiree oil pas-ses from heater |39 through line |45, vaive |45 and line |41 into storage tank |48. The vaporized propane from heater |39 passes by means of line |4| to compressor |42 Which forces it through lines |43 and 9 to condenser |20 where it is liqueed and passes by means of line |2| into propane storage tank H0,

It is to be understood that the foregoing example is merely illustrative of one method of carrying out my invention and must not be construed as limiting upon the invention which I claim as many modications will appear to those skilled in the art.

What I claim is: Y

1. A process for separatingwax from a wax-` oil mixture which comprises forming a chilled `mixture of separated wax and oil diluted with a liquefied normally gaseoushydrocarbon diluent having an average molecular weight greater than that of ethane and at leastas low as that' of butane and iiltering the chilled mixture to remove said separated wax from the diluted oil.

2. A process according to claim 1 in which the liqueed normally gaseous hydrocarbon diluent consists chieily of liquid propane.

3. A process of removing wax from a Wax-oil mixture which comprises diluting an oil-Wax mixture with a liqueiied hydrocarbon diluent which has a vapor pressurehigher than that of butane and lower thanthat of ethane, chilling the mixture to precipitate Wax and liltering the chilled mixture to remove the precipitated Wax from the chilled mixture.

4. A process of separating wax from a waxbearing oil'which comprises mixing said oil with a liquefied hydrocarbon diluent composed chiefly of propane and having a vapor pressure substantially equal to that of propane, chilling the mixture to precipitate Wax and filtering the chilled mixture to remove said precipitated Wax from the chilled mixture.

5. vA process of removing Wax from awax-oil mixture which comprises diluting an oil-Wax mixturewith a liquefied hydrocarbon `diluent which has a vapor pressure higher than that of butane and lower than that or ethane, evaporating a portion of said hydrocarbon diluent in direct contact with the oil-Wax mixture whereby the oil-wax mixture is chilled to precipitate the Wax and ltering the chilled mixture to remove the precipitated wax from the chilled mixture.

6. A process for separating Wax from a Waxoil mixture which comprises forming a chilled mixture of separated Wax and oil diluted with a liqueed normally gaseous hydrocarbon diluent having an average molecular Weight greater than that of ethane and'at least as loW as that of butane and filtering the chilled mixture in the presence vof a ilter aid to remove said separated Wax from the diluted oil.

7. A process for the separation of Wax from a wax-oil mixture which compris-es dissolving said oil under pressure in a liquefied normally `gaseous hydrocarbon diluent consisting predominantly of propane, releasing the pressure and vaporizing a portion of said diluent to lower the temperature of the Wax-oil mixture sufliciently to precipitate Wax, maintaining diluent in sufcient quantities to permit ready filtration, filtering the chilled mass through lter aid to remove the Wax and subsequently separating filtrate into diluent and dewaxed oil.

8. A process for the separation of Wax from a Wax-oil mixture which comprises diluting said Wax-oil mixture with a liquefied normally gaseous hydrocarbon diluent consisting preponderantly of propane under temperature and pressure conditions sufficient to prevent substantial evaporation of said liquid diluent, agitating the mixture and effecting solution of the Wax-oil mixture in the diluent, chilling the solution to a temperaturel suiiciently low to precipitate the Wax, maintaining the diluent in amount suiiicient to thin the oil to permit ready separation of the` Wax and ltering the chilled mixture tol remove the Wax from the diluted oil.

ULRIC B. BRAY. 

